Disposable absorbent articles have an absorbent structure for absorbing bodily exudates, a soft liquid-permeable top sheet on the wearer side and a liquid-impermeable back sheet on the garment side. The absorbent structure in between is normally made from a mixture of cellulose fibers or other fibrous substance and an absorbent polymer material. These fibrous substances make these absorbent articles typically quite fluffy and bulky.
In recent years there has been increasing demand for flexible, thinner, lightweight absorbent structures to resolve various problems of manufacturing, marketing, design, fit, wearing comfort, distribution, garbage disposal, material and energy consumption, transportation and storage costs and the like.
The most common method currently used to meet these demands in disposable absorbent articles is to reduce the amount of cellulose fibre or other support material within and surrounding the absorbent structure and/or use larger amounts of absorbent polymer materials. Consequently such absorbent articles have a smaller proportion of hydrophilic cellulose fibres and/or a higher proportion of absorbent polymers materials. Some of these absorbent articles may be better at storing liquid, however they are not necessarily good at absorbing and distributing liquid when the absorbent article is actually being used. It will thus be apparent from the above that the absolute and relative proportions of the fibrous material and absorbent polymer material are closely linked in light of article performance. Hence there are limits on reducing the amount of hydrophilic cellulose fibre and reducing the thickness of absorbent cores.
Many attempts have been undertaken to manufacture flexible, thin, lightweight absorbent structures, consisting of a high amount of absorbent polymer material. In order to obtain good absorbency, distribution and retention within such absorbent structures it has found to be important to at least partially immobilize the absorbent material. Failing to provide sufficient structural integrity results in loss of functional performance characteristics such as coherence, absorption, distribution and/or retention and results in failures related but not limited to for instance leakages, high rewet values, etc. On the other hand however the presence of this physical and/or chemical interaction in between the absorbent material and the restraining material often also leads to a reduced absorption, distribution and/or retention performance. This is especially the case when such flexible, thin, lightweight absorbent structures, consisting of an absorbent polymer material are placed in between multiple enveloping layers.
The larger proportion of absorbent polymer materials and related immobilisation requirements in substantially cellulose free absorbent articles may thus greatly inhibit the absorption, distribution and/or retention of liquids if inadequately managed. It will be clear that the absolute and relative proportions of the hydrophilic cellulose fibres and absorbent polymer materials need to be tightly controlled in order to maintain the absorbent properties of the absorbent structures. Certainly decreased absorption speed and fluid distribution are common causes of failure. Since such hygienic absorbent articles are generally also disposable and need in some instances to be worn over many hours they require performance in a dry state as well as in a partially and fully bodily exudates loaded state.
The ability and capacity of an absorbent polymer material to absorb, distribute and retain liquid is dependent upon the form, position and/or manner in which the absorbent polymer material is incorporated into the absorbent structure. Since many absorbent structures have a relatively homogeneous and continuous distribution of absorbent polymer material, and thus exhibit a substantial homogeneous swelling, for second, third and next liquid insults such absorbent layers may actually act as a liquid barrier. This gel-blocking occurs when the absorbent polymer material located in regions of first contact starts to increase in volume as a consequence of imbibing the fluid, thereby forming a hydro-gel. Gel blocking in and adjacent a zone of the absorbent layer of initial liquid contact prevents liquid from rapidly dispersing or wicking past the “blocking” material into the rest of the absorbent layer and further liquid uptake by the absorbent layer must then take place via for instance a diffusion process that is much slower than the rate at which liquid is applied to the absorbent layer. Especially when absorbent polymer material concentrations are absolutely or relatively high and wetted, the hydro-gel can block the initial and/or additional fluid from reaching other still more absorbent regions of the absorbent core, thus leading to unappreciated, underused or unused absorbent capacity. The diminished capacity results in leakages, well before the absorbent core is fully saturated.
Gel-blocking is even increased in thin substantially cellulose free structures where the liquid find little or limited macroscopic voids and/or spaces which can be used for temporary, intermediate or final liquid storage. Also the structural volume restrictions of these absorbent structures lead to a further reduced absorbent performance due to limited swelling capacity of the absorbent polymer material increasing the tendency to functional failures and leakages. To remedy, absorbent article designers have and typically use additional side cuffs and acquisition layers which are expensive, inefficient and can only partly remedy these limitations. By not completely abandoning the use of hydrophilic fibrous materials next to the use of absorbent polymer materials this problem can be partially resolved, however, it will be clear that in such case the absolute and relative proportions of absorbent materials will unwillingly be restricted and thus any thickness reduction of the absorbent structure not fully optimised.
It has been found in order to be able to keep absorbent materials compartmentalized, restrained and/or bound within the absorbent structures during use, it is preferred to deposit such absorbent material in a predetermined and desired location, grids or pattern during the manufacturing process. It is therefore very desirable to enable the depositing of absorbent materials in a substantially continuously, specific, well-defined and discretely arranged pattern onto a carrier layer moving at a relatively high speed.
The present invention is not only useful for the hygiene industry (e.g. for feminine hygiene garments, baby diapers and baby pants, adult incontinence garments) but may find applications in a multitude of industries such as the food industry (e.g. for coffee pads), the consumer industry (e.g. for disposable body warmers), the household industry (e.g. sheet formed detergent articles), construction (e.g. filter materials and insulation) as well as many other areas where it is desirable to deposit and immobilise particle materials on to a high-speed carrier layer.
Multiple attempts have been made to provide methods to manufacture composite structures with selected regions of particulate materials intermittently and discretely located along the length of a carrier layer. U.S. Pat. No. 5,494,622 describes a process and apparatus for forming sandwich-like structures having clusters of absorbent particulate material which are in a pattern chamber directly drawn and deposited on to the surface of the carrier layer by gas flow facilitated vacuum means. Due to the fact the pattern chamber is in contact with several pocket regions at a time, the filling of the pockets often results in under- and/or overfilling during the forming process leading to inefficient use of raw materials and leading to under-performing absorbent structures, structural failures and leakages. EP1621166 describes a process and apparatus for forming a substantially cellulose free sandwich-like structure having pre-metered clusters of absorbent particulate material held in pre-arranged patterns before being discretely deposited onto the carrier layer so as to have the same pre-measured clusters located in predefined patterns before being immobilised and enveloped between the carrier and cover material. Whilst the prior art attempts describe approaches to manufacture sandwich structures and mechanism to obtain discrete particulate material pockets, it is believed that the above methods suffer from multiple drawbacks. The prior art methods lack accuracy and repeatability of the absorbent particulate material patterns and have unbalanced pre-metering, metering, forming and transport means. The large and expensive pre-metering, forming and suction means required for the particulate material transport and clustering require very specific customization for each product concept/size/absorbency and are very expensive to design, build, install and replace. These apparatus are furthermore consuming a relative high amount of energy and take significant resources to operate during normal production. The web materials require operating within very narrow tolerances in relation to particle material clustering and depositing and can only operate under relatively limited production speeds, demanding large and complex machinery and installations which are subject to excessive tear, wear, maintenance, cleaning, adjustment, etc. Also, the prior art methods require the carrier layer to be at least sufficiently gas permeable, whilst it would be desired for many applications in fluid handling and storing products such as e.g. baby diapers that the carrier layer would be composed of a liquid and substantially gas impervious barrier layer. Such inefficient and ineffective methods and the complex manufacturing processes makes neither of the prior art methods economically, technically and/or environmentally advantageous.
Hence, there is still a need in the art for a reliable, cost-efficient and maintenance-friendly method and apparatus to consistently dispose, position and pocket particulate materials continuously in a specific, well-defined and discretely arranged pocketing pattern on the surface of a carrier layer moving at a high production speed with limited consumption and/or waste of resources such as e.g. energy and raw materials enduring the production process.
As a result of exhaustive research to address the above-identified and related problems, the inventor have found a more favorable and advantageous manufacturing process to obtain such concepts and structures, which will be explained in greater detail down below.